The present invention relates to a multilayer barrier film with very good thermo-forming properties especially on form-, fill- and seal-machines (FFS-machines). The film has paper-like features.
In the food-processing industry perishable products, as for example fresh meat, poultry, fish, cheese and products made from these products, are packed in so-called barrier films. These kinds of food are either packed in a defined gas-atmosphere (MAP-packages=Modified Atmosphere Packages) or in a vacuum (vacuum-packages). Therefore, in MAP-packages the surrounding atmosphere is replaced by various gas mixtures depending on the product. Typical examples for gas compositions are CO2/O2 mixtures for fresh meat, and gas mixtures of CO2 and N2 for sliced meat. According to that, films with barrier properties must be used as packaging material in relation to the gases mentioned above.
The food products named above as examples can also be vacuum-packed. According to this packaging process the surrounding atmosphere is nearly completely extracted from the packages. Barrier films, which avoid oxygen transfer from the surroundings into the packages, are used as packaging material. A high precentage of MAP- as well as vacuum-packages are produced on FFS-machines. As the geometry of the packages, in dependence on the goods to be packed, is formed by thermo-forming directly before the filling step, this packaging process is characterized by a high flexibility.
There is a variety of films, especially of barrier films, known for packaging. Thus, a transparent film has been known for a long time with the principal structure: polyamide (PA)/ethylene/vinyl alcohol (EVOH)/polyethylene (PE) or polystyrene (PS)/ethylene/vinyl alcohol (EVOH)/polyethylene (PE) or polyester terephthalate (PET)/poly vinylidene chloride (PVDC)/polyethylene (PE).
A non-transparent, white film is also known for packaging purposes. In EP 0161035 a 7-layer film filled with inorganic filler and comprising a barrier layer is described. It has no sealing layer and its thermo-formability is insufficient.
In EP 0494594 (see U.S. Pat. No. 5,248,534) a multilayer barrier film with a filled layer is disclosed which does not need an adhesive layer between the individual layers of the film. Based on the fact that the respective neighboring layers of the film are composed to some extent of the polymer of the neighboring layer, an adhesion between these layers is achieved after extruding, pressing together and cooling of these respective layers of the film.
These kinds of film also show the disadvantage of not being sufficiently thermo-formable.